The present invention relates to a magnetron plasma processing apparatus for processing a target substrate such as a semiconductor wafer with a magnetron plasma.
In recent years, a magnetron plasma etching apparatus for performing micropattern etching by generating a high-density plasma in a comparatively low-pressure atmosphere has been put into practical use. In this apparatus, a permanent magnet is arranged above a chamber. The magnetic field produced by the permanent magnet is applied horizontally to a semiconductor wafer. An RF electric field perpendicular to the magnetic field is simultaneously applied to the semiconductor wafer. The drift motion of electrons caused upon application of the magnetic and electric fields is utilized to etch the semiconductor wafer with a very high efficiency.
In the magnetron plasma, what contributes to the drift motion of electrons is a magnetic field perpendicular to the electric field, i.e., a magnetic field horizontal to the semiconductor wafer. As a uniform horizontal magnetic field is not always formed in the above apparatus, plasma uniformity is not sufficient. Thus, a nonuniform etching rate, charge-up damage, and the like may occur.
In order to avoid these problems, formation of a horizontal magnetic field uniform with respect to the semiconductor wafer in the processing space in the chamber is sought. As a magnet that can generate such a magnetic field, a dipole ring magnet is known. As shown in FIG. 9, this dipole ring magnet 102 is formed by arranging a plurality of anisotropic segment columnar magnets 103 in a ring-like shape outside a chamber 101. The directions of magnetization of the plurality of anisotropic segment columnar magnets 103 are slightly shifted from each other to form a uniform horizontal magnetic field B as a whole. FIG. 9 is a view (plan view) of the apparatus seen from above. The proximal end side of the direction of the magnetic field is indicated by N, the distal end side thereof is indicated by S, and positions separated 90xc2x0 from N and S are respectively indicated by E and W. In FIG. 9, reference numeral 100 denotes a semiconductor wafer.
The horizontal magnetic field formed by the dipole ring magnet in this manner is a horizontal magnetic field directed only in one direction of from N to S in FIG. 9. Accordingly, electrons travel in one direction by drift motion, causing nonuniformity in the plasma density. More specifically, the electrons drift in the direction of the outer product of the electric field and the magnetic field. In other words, when the electric field is formed to extend downward from above, the electrons travel from the E pole side to the W pole side by drift motion. Consequently, the plasma density is low on the E pole side and high in the W pole side, resulting in nonuniformity.
To prevent this, the dipole ring magnet is rotated in its circumferential direction to form a rotating magnetic field, so the direction of drift motion of electrons is changed. In practice, however, this cannot make the plasma density sufficiently uniform over a wide range.
A technique has been proposed in which a magnetic field gradient is formed in the drift direction of electrons, i.e., in a direction from the E pole side to the W pole side in FIG. 9, so the nonuniformity of plasma accompanying the drift motion of electrons is eliminated (Jpn. Pat. Appln. KOKAI Publication No. 9-27278). According to this technique, as shown in FIG. 10, the number of anisotropic segment columnar magnets on the W pole side is made smaller than that on the E pole side. As a result, a gradient is formed in which the magnetic field strength increases in the direction from the E pole side to the W pole side.
In recent years, devices have been required to shrink more and more in feature size, and a plasma etching process in a lower pressure has been required. To perform an efficient plasma process in a low pressure, the plasma density must be further increased. For this purpose, in the magnetron plasma process, the magnetic field strength may be increased.
When, however, an insulating film such as an oxide film is to be etched, to avoid charge-up damage, the magnetic field strength of that portion where a wafer is present is limited to about 200 Gauss at maximum. Even when a magnetic field gradient is formed by the above technique and plasma uniformity can be achieved, the plasma density cannot be sufficiently increased, and the etching rate may not be sufficiently high. If a region where the magnetic field is locally strong can be formed outside the E pole-side end of the wafer, the plasma density may be increased without damaging the wafer. Conventionally, however, it is difficult to locally form a strong magnetic field portion.
It is an object of the present invention to provide a magnetron plasma processing apparatus which can form a locally strong magnetic field portion at a desired position in a processing space for a target object, so the plasma density of the processing space can be increased.
According to a first aspect of the present invention, there is provided a magnetron plasma processing apparatus which comprises
a chamber with an outer wall that can maintain a reduced pressure,
process gas supply means for supplying a process gas into the chamber,
a pair of electrodes arranged in the chamber to oppose each other and to define a processing space therebetween,
electric field forming means for applying a voltage to the pair of electrodes, thus forming an electric field in the processing space, and
magnetic field forming means for forming, in the processing space, a magnetic field perpendicular to the direction of the electric field and directed in one direction, and which subjects a target substrate to a magnetron plasma process while the target substrate is set in the processing space to be parallel to the electrodes,
the magnetic field forming means having a dipole ring magnet including a plurality of first anisotropic segment magnets arranged in a ring-like shape around the outer wall of the chamber so as to form a magnetic field gradient, within a plane perpendicular to the direction of the electric field, such that a magnetic field strength is large and small on upstream and downstream sides, respectively, in an electron drift direction along a direction perpendicular to a direction of the magnetic field,
at least one second anisotropic segment magnet, arranged in the vicinity of a predetermined region located outside that end of the target substrate which is on the upstream side in the electron drift direction, with an N pole thereof being directed toward the predetermined region, and
at least one third anisotropic segment magnet arranged in the vicinity of the predetermined region with an S pole thereof being directed toward the predetermined region,
the second and third anisotropic segment magnets serving to locally increase the magnetic field strength of the predetermined region to be larger than that formed by the first anisotropic segment magnets.
According to a second aspect of the present invention, there is provided a magnetron plasma processing apparatus which comprises
a chamber which has an outer wall and can maintain reduced pressure,
process gas supply means for supplying a process gas into the chamber,
a pair of electrodes arranged in the chamber to oppose each other and to define a processing space therebetween,
electric field forming means for applying a voltage to the pair of electrodes, thus forming an electric field in the processing space, and
magnetic field forming means for forming, in the processing space between the pair of electrodes, a magnetic field perpendicular to the direction of the electric field and directed in one direction, and which subjects a target substrate to a magnetron plasma process while the target substrate is set in the processing space to be parallel to the electrodes,
the magnetic field forming means having a dipole ring magnet including a large number of anisotropic segment magnets arranged in a ring-like shape around the outer wall of the chamber, to form a magnetic field gradient, within a plane perpendicular to the direction of the electric field between the electrodes, such that the magnetic field strength is large and small on upstream and downstream sides, respectively, in an electron drift direction along a direction perpendicular to the direction of the magnetic field, and
the plurality of anisotropic segment magnets including a first portion including at least one anisotropic segment magnet arranged in the vicinity of a first region located outside that end of the target substrate which is on the upstream side in the electron drift direction with an N pole thereof being directed toward the first region, and a second portion including at least one anisotropic segment magnet, arranged in the vicinity of a second region located outside that end of the target substrate which is on the upstream side in the electron drift direction, to be away from the first region, with an S pole thereof being directed toward the second region, the first and second portions serving to locally increase magnetic field strengths of the first and second regions.
With the above arrangement, a strong magnetic field portion can be locally formed at a predetermined region located outside that end of the target substrate which is on the upstream side in the electron drift direction. The plasma density of the processing space can accordingly be increased.
Preferably, the anisotropic segment magnets are arranged such that gaps among those which are on the upstream side in the electron drift direction are narrower than gaps among those which are on the downstream side in the electron drift direction.
The anisotropic segment magnets preferably form a magnetic field with 200 Gauss at maximum, preferably 100 Gauss to 200 Gauss, at a portion thereof opposing the target substrate, and a magnetic field of at least 200 Gauss, preferably 200 Gauss to 400 Gauss, at the predetermined region.